Los Blancos were held to a goalless draw by Valencia at the Bernabeu on Sunday to leave
themselves just four points clear of defending champions Barcelona at the top.

"Real Madrid
can lose the league title because we haven't won it yet mathematically and there
is a team close behind that also have a lot at stake," Casillas said.

"We cannot live just on the fact that our lead used to be ten and eight points
strong.''

Jose Mourinho's Real side have now dropped six points in their last five games,
while they still have to face Barcelona at the Nou Camp later this month.

But Casillas feels the players have to put their most recent disappointment behind
them and focus on the Madrid derby against Atletico on Wednesday.

"We had more chances than Valencia, but they also had several and we could
have dropped more points,'' he said on the club's website.

"Mentality is very important. The lead we had has been reduced, but we
shouldn't cry about it. We have a large lead, but it isn't definitive and we
must continue focusing on one game at a time.

"We must focus on winning against Atletico Madrid. This moves very quickly and
we play many games in few days. We have to go on.

"The derby will be a difficult match and we expect Atletico to be motivated,
especially after their defeat against Levante and because they haven't defeated
us in a very long time.

"They've reached the Europa League semi-finals and they have to continue
winning in order to stay at the top of their game.

"Every match is vital and they'll all be like finals, so we'll think about
Bayern Munich (in the Champions League semi-finals), Sporting (Gijon) and
Barcelona after facing Atletico, who are the ones that matter to us right now.

Madrid assistant coach Aitor Karanka claimed his side were looking forward to
getting their title push back on track on Wednesday.

"Our players gave it all in 95 minutes and had many chances to score
throughout the match,'' Karanka said.

"The crowd was there for us and the only thing we said in the dressing room
after the game was that we must now focus on our next match.

"The squad wants to play the next game. The players are looking forward to
winning and continue working hard. The only thing left to do when wearing this
shirt and crest is to keep fighting.

"The squad is united and looking forward to it. We have chances to win the
title and we want to play to the end.''